Electronically switchable privacy film and display device having same

ABSTRACT

An electronically switchable privacy films suitable for use in display devices are described. The electronically switchable privacy film comprises a pair of mutually opposing transparent electrodes; an optically transparent microstructured layer disposed between the transparent electrodes, the microstructured layer comprising a plurality of microstructured ribs extending across a surface thereof such that the microstructured ribs form an alternating series of ribs and channels; and electronically switchable material disposed in the channels, the electronically switchable material being capable of modulation between high and low absorption states upon application of an electric field across the transparent electrodes.

FIELD OF INVENTION

This disclosure relates to optical films, particularly privacy filmswhich can be used with electronic display devices.

BACKGROUND

Privacy films are known in the art of electronic display devices. Aviewer can apply a privacy film to the viewing surface of an electronicdisplay device such that images can be viewed selectively. Typically,when the viewer is positioned within a range of small viewing anglesrelative to the normal of the surface of the privacy film, images beingdisplayed are viewable through the film. As the position of the viewerchanges such that the viewing angle increases relative to the normal,the amount of light transmitted through the privacy film decreases untila maximum viewing angle is reached and images being displayed are nolonger viewable.

SUMMARY

An electronically switchable privacy film is disclosed. The film can beused in a privacy mode when a user wishes to restrict viewing ofinformation being displayed by an electronic display device. When theuser wishes to share information being displayed, the electronicallyswitchable privacy film can be switched to a public mode for sharing.The viewer can switch back and forth between modes without having tophysically remove the film from the viewing surface of the displaydevice.

The electronically switchable privacy film can be used in differentways. For example, the film may be applied to the viewing surface of adisplay device and powered by a USB adapter with the use of a built-intransformer circuit. The electronically switchable privacy film may alsobe incorporated into a display device during manufacture of the device,for example, between a display panel and an outer viewing surface of thedevice, such as a touch screen. When built into a display device, thepower for the privacy film could be drawn from a battery or electricaloutlet. Such a display device would have built-in public and privacymodes, and a consumer would not need to purchase and install a separateprivacy film.

The electronically switchable privacy film comprises a pair of mutuallyopposing transparent electrodes and an optically transparentmicrostructured layer disposed between the transparent electrodes, themicrostructured layer comprising a plurality of microstructured ribsextending across a surface thereof such that the microstructured ribsform an alternating series of ribs and channels. The film compriseselectronically switchable material disposed in the channels of themicrostructured layer. The electronically switchable material is capableof modulation between high and low absorption states upon application ofan electric field across the transparent electrodes. The electronicallyswitchable privacy film preferably comprises certain transmissionproperties. When the electric field is not applied, the film is in aprivacy mode such that it has a light transmission of less than about10% at a viewing angle of 30°. When the electric field is applied, thefilm is in the share mode such that it has an increase in lighttransmission and the difference in transmission between the privacy modeand share mode is at least 5% for viewing angles from about 30 to about45°. The film has a light transmission of at least about 25% in shareand privacy modes at viewing angles from 0 to about 15°. These and otheraspects of the invention are described in the detailed descriptionbelow. In no event should the above summary be construed as a limitationon the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description in connection with the following figures.The figures are not necessarily drawn to scale.

FIGS. 1A and 1B show schematic cross-sectional and perspective views,respectively, of exemplary optical films from which the electronicallyswitchable privacy film can be made.

FIG. 2 shows schematic cross-sectional views of an exemplaryelectronically switchable privacy film illustrating electronicswitchability of the film between privacy and share modes.

FIGS. 3 and 4 show schematic cross sectional views of exemplary opticalfilms from which the electronically switchable privacy film can be made.Selected geometrical parameters of the films are shown.

FIG. 5 shows a schematic cross sectional view of an exemplaryelectronically switchable privacy film.

FIG. 6 shows normalized transmission as a continuous function of viewingangle for the electronically switchable privacy film of Example 1.

FIG. 7 shows images of an exemplary electronically switchable privacyfilm used with a standard eye chart.

FIG. 8 shows schematic representations of an exemplary electronicallyswitchable privacy film used with an exemplary electronic displaydevice.

FIG. 9 is a cross-sectional view of an electron display devicecomprising an electronically switchable privacy film.

DETAILED DESCRIPTION

Privacy films are known and are purchased generally as aftermarket itemsfor use with electronic display devices, particularly when one does notwant others to see the contents of the screen. A user physically appliesthe privacy film to the viewing surface of his display device, and theinformation being displayed on the viewing surface can be viewed onlywithin a range of angles referred to herein as “viewing angle”.Typically, the viewing angle is some range of angles centered on an axisnormal to the privacy film, for example, 0°+/−30°. Many types of privacyfilms can be characterized as “static” privacy films having a singleprivacy mode. If the viewing surface is covered with a static privacyfilm, and the user wants others to see the contents of the screen, theprivacy film needs to be physically removed from the surface and storedin a location where it does not become damaged.

One type of static privacy film comprises a transparent louver filmdisposed on a polymeric substrate, with light absorbing materialdisposed in channels formed between the louvers such that alternatingtransparent and light absorbing regions are formed. The transparent andlight absorbing regions are relatively positioned to provide arestricted viewing angle. An exemplary privacy film of this type isdescribed in U.S. Pat. No. 6,398,370 B1 (Chiu et al.).

The electronically switchable privacy film disclosed herein is differentfrom a conventional privacy film, such as a static privacy film, becausea user can switch between share and privacy modes without having toremove the film from the viewing surface of his display device.Switching can be carried out via an external hardware orsoftware-controlled switch electrically coupled to the film. In someembodiments, in the presence of an electric field, the electronicallyswitchable privacy film is in the share mode, and in the absence of anelectric field, the film is in the privacy mode. Thus, a user can switchback and forth between the two modes by changing the strength of theelectric field.

FIG. 1A shows a schematic cross-sectional view of an exemplary opticalfilm from which the electronically switchable privacy film can be made.Optical film 10 comprises transparent electrode 11 and opticallytransparent microstructured layer 12 disposed on the electrode. Theoptically transparent microstructured layer comprises a plurality ofmicrostructured ribs 14 extending across surface 13 of the layer. FIG.1B shows an embodiment of optical film 10 wherein microstructured ribs14 extend across major surface 13 of the optically transparentmicrostructured layer such that an alternating series of ribs 14 andchannels 15 are formed.

FIG. 2 shows schematic cross-sectional views of an exemplaryelectronically switchable privacy film illustrating electronicswitchability of the film between privacy and share modes.Electronically switchable privacy film 20 comprises pair of mutuallyopposing transparent electrodes 21 and 22 and optically transparentmicrostructured layer 23 disposed between the electrodes. The opticallytransparent microstructured layer comprises plurality of microstructuredribs 24 extending across a surface of the layer, for example, as shownin FIG. 1B such that an alternating series of ribs 24 and channelscomprising electronically switchable material 25 are formed. Theelectronically switchable material is capable of modulation between highand low absorption states upon application of an electric field acrosstransparent electrodes 21 and 22. For the embodiment shown in FIG. 2,electronically switchable material 25 is shown schematically as rod-likemolecules, such as liquid crystals, which can be randomly oriented 25 ain the absence of an electric field, and substantially oriented 25 b inthe presence of an electric field.

Geometrical parameters which influence performance of privacy films havebeen described, for example, see US 2010/0271721 (Gaides et al.);incorporated herein by reference. Therefore, only a brief explanation ofthese parameters in the context of privacy film performance is provided.Geometrical parameters described herein are illustrated in FIG. 3. FIG.3 shows a schematic cross sectional view of an exemplary privacy film 30comprising optically transparent microstructured layer 33 disposedbetween opposing transparent electrodes 31 and 32. The opticallytransparent microstructured layer comprises a plurality ofmicrostructured ribs 34 extending across a surface of the layer, forexample, as shown for optical film 10 in FIG. 1B. Channels 35 are formedbetween adjacent ribs and comprise electronically switchable material(not shown). Each rib/channel has height H, each rib has width W, andpitch P indicates spacing of the channels. Width Y of the channels isP−W. Optically transparent microstructured layer 33 also comprises land36 having height L such that the thickness of layer 33 is H+L. Thespacing and shape of the ribs determine viewing angle θ_(V). Rib aspectratio for layer 33 is defined as H/W, and channel aspect ratio as H/Y.

Parameters H, W, P, Y and L of the optically transparent microstructuredlayer can have any suitable values as long as the electronicallyswitchable privacy film can function as desired. In general, dimensionsof the ribs are selected such that the desired viewing angle is providedby the film. At the same time, it is desirable for the parameters to beselected such that an adequate amount of light can pass through the filmand toward the viewer. Smaller channel widths and larger pitch can leadto increased on-axis transmission, while deeper channels lead toincreased off-axis optical scattering or absorption.

In some embodiments, each rib has height H from about 10, 15, 20 or 25to about 150 μm and width W from about 25 to about 50 um. In someembodiments, rib aspect ratio H/W is greater than about 1.5, forexample, greater than about 2.0, or greater than about 3.0. For example,each rib may have height H from about 25 to about 150 um and width Wfrom about 25 to about 50 um such that rib aspect ratio H/W is greaterthan about 1.5.

In some embodiments, each channel has height H from about 25 to about150 μm and width Y from about 1 to about 50 um. In some embodiments,channel aspect ratio H/Y is greater than 3, 4, or 5. In someembodiments, the channel aspect ratio can be at least 6, 7, 8, 9, or 10.The channel aspect ratio is typically no greater than 50. When thechannel aspect ratio is sufficiently high and the channels comprise alight absorbing material such as a dichroic dye, the privacy filmexhibits low transmission (e.g. less than about 10%) at a viewing angleof 30° when an electric field in not applied and the film is in (e.g.static) privacy mode. In privacy mode, the transmission typicallydecreases as the angle increases from 30 to 60 degrees. Hence, when theprivacy film exhibits low transmission (e.g. less than about 10%) at aviewing angle of 30°, the film also exhibits low and typically evenlower transmission at viewing angles greater than 30°.

The height of the land (L) is typically minimized provided that the landis sufficiently thick such that it can support a large number of ribs,yet thin enough so that it does not interfere with optical andelectrical switching performance of the privacy film.

The microstructured ribs may have sides or walls that are substantiallyparallel to each other or they may be angled. FIG. 4 shows a schematiccross sectional view of an exemplary privacy film 40 comprisingoptically transparent microstructured layer 43 disposed between opposingtransparent electrodes 41 and 42. The optically transparentmicrostructured layer comprises plurality of microstructured ribs 44 andchannels 45 disposed between the ribs and comprising electronicallyswitchable material (not shown). Each microstructured rib has angledwalls 46 a and 46 b, and each wall has wall angle θ_(W). The wall anglecan be used to vary the viewing angle as described, for example, in US2010/0271721 (Gaides et al.). In some embodiments, the wall angle isless than about 6°.

The optically transparent microstructured layer is generally anoptically transparent layer with desired light transmittance over arange of angles and wavelengths. The optically transparentmicrostructured layer can have light transmittance from about 80 toabout 100% over at least a portion of the visible light spectrum (about400 to about 700 nm). In some embodiments, the optically transparentmicrostructured layer has a haze value from about 0.1 to less than about5%. In some embodiments, the optically clear microstructured layerexhibits light transmittance from about 80 to about 100% and a hazevalue from about 0.1 to less than about 5%.

In some embodiments, the optically clear microstructured layer has arefractive index from about 1.48 to about 1.75, or from about 1.48 toabout 1.51. In some embodiments, the optically clear microstructuredlayer has a refractive index which closely matches that of theelectronically switchable material in the presence of an electric field.For example, in some embodiments, the refractive index differencebetween the optically transparent microstructured layer and theelectronically switchable material is less than about 0.05 when the filmis in the share mode. In some embodiments, the refractive indexdifference between the optically transparent microstructured layer andthe electronically switchable material is greater than about 0.05 whenthe film is in the privacy mode.

The optically transparent microstructured layer can comprise anymaterial as long as the desired properties of the optically transparentlayer are obtained. Typically, the optically transparent microstructuredlayer is generally made from a polymerizable composition comprisingmonomers which are cured using actinic radiation, e.g., visible light,ultraviolet radiation, electron beam radiation, heat and combinationsthereof, or any of a variety of conventional anionic, cationic, freeradical or other polymerization techniques, which can be chemically orthermally initiated.

Useful polymerizable compositions comprise curable groups known in theart such as epoxy groups, ethylenically unsaturated groups, allyloxygroups, (meth)acrylate groups, (meth)acrylamide groups, cyanoestergroups, vinyl ether groups, combinations of these, and the like. Themonomers used to prepare the optically clear microstructured layer cancomprise polymerizable oligomers or polymers such as urethane(meth)acrylates, epoxy (meth)acrylates, polyester (meth)acrylates) asdescribed in U.S. Pat. No. 6,398,370 B1 (Chiu et al.), US 2010/0201242(Liu et al.), US 2010/0271721 A1 (Gaides et al.) and US 2007/0160811 A1(Gaides et al.).

The optical film shown in FIG. 1A can be made using a coating process asdescribed, for example, in U.S. Pat. No. 4,766,023 (Lu et al). In thisprocess, a transparent electrode is coated with an acrylic monomercomposition as described, for example, in US 2007/0160811 A1 (Gaides etal.). The composition is polymerized with high intensity UV radiationwhile pressed against a copper tool embossed with a microstructuredpattern. The cured composition in the form of a microstructured layer isreleased from the tool. Release can be facilitated by use of a releaseagent coated on the surface of the copper tool. Release can also befacilitated by suitable design of the channels as described, forexample, in U.S. Pat. No. 6,398,370 B1 (Chiu et al.) wherein the channelwalls are angled at a few degrees relative to the surface normal.

The particular combination of monomers used to form the cured polymericlayer may be selected such that the modulus of the layer is low enoughto enable release from the tool, but with enough cohesive strength notto break during roll to roll processing. If the cured polymeric layer istoo soft, it will cohesively fail, but if it is too brittle, it willfracture or not pull out of the tool. The combination of monomers may beselected such that the cured polymeric layer sufficiently adheres to thetransparent electrode on which it is formed.

In general, the electronically switchable material can comprise anyelectronically switchable material which is capable of modulationbetween high and low absorption states upon application of an electricfield between the transparent electrodes. Various electronicallyswitchable materials are known such as liquid crystals andelectrochromic systems.

The electronically switchable material may comprise any suitable liquidcrystals such as chiral liquid crystals, nematic liquid crystals or acombination of chiral and nematic liquid crystals. In most cases, it isdesirable that the liquid crystals in the presence of the electric fieldexhibit substantially uniform alignment. Exemplary liquid crystals canhave a chemical structure based on a core of aromatic or cycloaliphaticgroups which can be connected by linkage groups and terminated by sidechain and terminal groups. Cycloaliphatic components include saturatedcyclohexanes, and aromatic components include phenyl, biphenyl, andterphenyl units in various combinations. Examples of side chain andterminal groups are alkyl (C_(n)H_(2n+1)), alkoxy (C_(n)H_(2n+1)O), andothers such as fluoroalkoxy, acyloxyl, alkylcarbonate, alkoxycarbonyl,nitro and cyano groups. The linkage groups can contain single bonds(—C—C—) double bonds (—CH═CH—), triple bonds (—C≡C—), or any combinationthereof, or may contain ester groups (O—C═O), azo (—N═N—), or Schiffbase (—CH═N—) groups. Other liquid crystals which may be useful includeheterocyclics, organometallics, sterols, and some organic salts of fattyacids.

Usually, in the case of liquid crystals (LC), the electronicallyswitchable material exhibits dielectric and optical anisotropy. Thedielectric behavior of liquid crystals is related to the molecules'response to an electric field. Dielectric permittivity is a physicalquantity that describes how an electric field affects the said mediumand is determined by the ability of the medium to polarize in responseto an applied electric field. The medium reacts such that the fieldinside the material is partially cancelled. Dielectric anisotropy (Δ∈)is defined as the difference in dielectric permittivity of the LCmolecule parallel to the long axis director (∈_(|)) and the dielectricpermittivity perpendicular to the LC director (∈_(⊥)), orΔ∈=∈_(|)−∈_(⊥). Therefore, the value of dielectric anisotropy can bepositive or negative. LC molecules with positive dielectric anisotropywill align parallel to the direction of the electric field, whereas LCmolecules with negative dielectric anisotropy will align perpendicularto the applied electric field. The magnitude of the dielectricanisotropy, i.e., the absolute value of the dielectric anisotropy,defines the sensitivity with which the molecule is able to respond toelectric field, such that the greater the magnitude of the dielectricanisotropy, the lower the voltage required for switching.

There are certain optical properties which are also associated with thedifferent orientations of the liquid crystal molecules. Due to thetypically rod-like shape of liquid crystal molecules, such molecules canbe characterized as having a long and short axis. The index ofrefraction of light is different along each axis of the liquid crystalmolecule, such that the liquid crystals are said to exhibit opticalanisotropy. For example, randomly oriented liquid crystal molecules haveeffective refractive index, n_(eff). The effective refractive index isan ensemble average of characteristic ordinary (n_(o), director parallelto long axis of molecule) and extraordinary (n_(e), director parallel toshort axis of molecule) refractive indices of the liquid crystals,wherein (n_(eff)=(n_(o)+n_(e))/2). In some embodiments, the liquidcrystals have a range of refractive indices from about 1.52 (n_(o)) toabout 1.75 (n_(e)). Therefore, in some embodiments, n_(eff) is about1.64. The effective refractive index comes into play when no electricfield is applied to the liquid crystals, as in privacy mode. When therefractive index of the liquid crystal is substantially different thanthat of the microstructured ribs, optical scattering between theinterfaces can occur, increasing haze and decreasing the transmission oflight through the film. When an electric field is applied to the liquidcrystals (e.g. share mode) the long axis of the liquid crystal moleculesalign parallel to the electric field lines, and the ordinary refractiveindex (n_(o)) comes into effect. Now, the refractive index of themicrostructured ribs matches closely with that of the liquid crystals,and light passes through the privacy film. This operating principle isdepicted in FIG. 2.

When the electric field is not applied, the film is in a privacy modesuch that it has a light transmission of less than about 10% at aviewing angle of 30°. When the electric field is applied, the film is inthe share mode such that it has an increase in light transmission andthe difference in transmission between the privacy mode and share modeis at least 5% for viewing angles from about 30 to about 45°. The filmhas a light transmission of at least about 25% in share and privacymodes at viewing angles from 0 to about 15°. The difference between thehaze of the electronically switchable privacy films in privacy mode ascompared to share mode in typically at least −15% (i.e. a decrease of15%) or −20% at a viewing angle of 30 degrees. In some embodiments, thedifference between the haze of the electronically switchable privacyfilms in privacy mode as compared to share mode is at least −30% or −35%at a viewing angle of 30 degrees. The difference in haze at 30 degreebetween privacy and share mode is typically no greater than −50%.

When using liquid crystals as the electronically switchable material,the electric field to which the electronically switchable materialresponds may be determined by the distance between the transparentelectrodes which may be from about 50 to about 150 um, and the voltageapplied to the electrodes which may be about 220V or less. The voltagenecessary to provide the necessary electric field may be determined bythe distance between the transparent electrodes and the dimensions ofthe channels.

The electronically switchable material may be selected such that whenthe electric field is applied, the electronically switchable privacyfilm is in the share mode such that it has an increase in lighttransmission and the difference in transmission between the privacy modeand share mode is at least 5% for viewing angles from about 30 to about45°. For some embodiments, the difference is at least 6%, 7%, 8%, 9% or10%. When in share mode, the transmission is typically at least 10% to15% for angles ranging from 30 to 45 degrees. In some embodiments, thetransmission of the privacy film in share mode is no greater than 40%,or 35%, or 30%, or 25% for angles from 30 to 45 degrees.

The electronically switchable material may comprise any suitablematerial which is stable under the operating conditions of the displaydevice within which the privacy film is used. As such, suitableelectronically switchable materials may be stable under continuousexposure to UV and visible light as well as radiant heat.

The liquid crystals may be used in any amount relative to the totalweight of the electronically switchable material as long as the desiredproperties of the material can be obtained. For example, theelectronically switchable material may comprise liquid crystals in anamount from about 90 to about 99 wt. % relative to the total weight ofthe material.

In some embodiments, the electronically switchable material comprises a“guest-host” mixture of dichroic dye mixed in with the liquid crystals.In these systems, the long axis director of the liquid crystals alignsin the direction of the field lines during electrical activation. Thedye molecules rotate along with the director of the liquid crystalsduring electrical activation, amplifying the effect of the transmissionchange between the on and off states.

Suitable dichroic dyes include those having a large dielectricanisotropy due to the presence of a strong on-axis dipole moment. Forexample, the dielectric anisotropy of the dichroic dye may be at leastthat of the liquid crystals. Other desirable properties of dichroic dyeswhich are suitable for use in the electronically switchable materialinclude those which are stable to continuous exposure to UV and visiblelight, have a high dichroic ratio, good solubility in the liquidcrystalline media, and have a high extinction coefficient. Suitabledichroic dyes comprise black dyes or any combination of red, yellow,green, etc. dyes which provide absorption characteristics of a blackdye. The dichroic dye may be used in any amount as long as theelectronically switchable material can exhibit the desired properties,for example, from about 0.1 to about 10 wt-% relative to the totalweight of the electronically switchable material.

The strength of the coupling between the liquid crystals and dyemolecules is referred to as the order parameter. Perfect couplingbetween the liquid crystals and dye molecules is indicated by an orderparameter of 1, and usually it is desirable for the order parameter tobe as close to 1 as possible such that absorption of light by the dyemolecules is minimal in the share mode. The order parameter may be fromabout 0.6 to 1.0, or from about 0.7 to about 0.9. One example of anelectronically switchable material comprises a mixture of nematic liquidcrystals and dichroic black dye which is available as “ZLI-4727” fromMerck KGaA (Darmstadt, Germany).

The electronically switchable material may comprise a chiral dopantwhich lowers the threshold of voltage that needs to be applied betweenthe transparent electrodes in order for switching between privacy andshare modes. The chiral dopant may comprise a mixture of a chiraladditive and nematic liquid crystals. Useful chiral dopants includethose having a dielectric anisotropy greater than about 30, or fromabout 30 to about 80. The amount of chiral dopant used in theelectronically switchable material depends on the particular nature ofthe material; typically, the amount of chiral dopant can be up to about40 wt. % relative to the total weight of the electronically switchablematerial.

Chiral liquid crystal molecules give rise to a phase in which themolecules twist perpendicular to the director, with the molecular axisparallel to the director. The chiral pitch (p) refers to the distanceover which the liquid crystal molecules undergo a full 360° twist. Thepitch changes when the temperature is altered or when other moleculesare added to the liquid crystal host, such as an achiral material,allowing the pitch to be tuned accordingly. In some embodiments of theswitchable privacy film, the pitch length of the liquid crystalcompositions may be greater than about 800 nm, for example, from about800 to about 1500 nm, which increases absorption at all viewing anglesin the absence of an electric field.

In some embodiments, the magnitude of the dielectric anisotropy for theelectronically switchable material is greater than about 20, greaterthan about 25, or greater than about 30 as measured at 1 KHz and 20° C.In one embodiment, the electronically switchable material comprises amixture of a first electronically switchable (e.g. liquid crystal)material having a relatively low dielectric anisotropy and a secondelectronically switchable (e.g. chiral dopant) material having a highdielectric anisotropy such that the magnitude of the dielectricanisotropy of the mixture is greater than about 20, greater than about25, or greater than about 30, as previously described. The firstelectronically switchable (e.g. liquid crystal) material may have adielectric anisotropy of less than 15, or 10 and the secondelectronically switchable (e.g. chiral dopant liquid crystal) materialmay have a dielectric anisotropy of at least 30, 40, 50, or 60 asmeasured at 1 KHz and 20° C. For example, in some embodiments, a highdielectric anisotropy material, such as “MDA-04-927” (Merck KGaA) wasused in a matrix of a lower dielectric anisotropy dichroic nematicliquid crystal component, such as “ZLI-4727”. However, the ZLI-4727material by itself did not provide significant optical switching uponapplication of an electric field.

The electronically switchable material may also comprise apolymer-dispersed liquid crystal (PDLC) composition. PDLC constructionsoffer an enhancement in the durability and ease of handling of theswitchable privacy film. In PDLC constructions, a mixture of a liquidcrystal material solubilized in a polymerizablemonomer/crosslinker/photoinitiator combination is loaded into channelsof a film and cured using UV radiation. The growth in molecular weightof the polymer upon curing induces demixing, creating ‘droplets’ ofliquid crystals dispersed in a polymer matrix. Typically, a polymermatrix is selected which features a similar refractive index (n_(p)) tothe ordinary axis of the liquid crystal (n_(o)=n_(p)) in order tominimize haze in the share mode. The size of the liquid crystal dropletscan be controlled based on the monomer functionality and intensity ofradiation used for curing. If designed correctly, smaller droplet sizeleads to many polycrystalline regions of randomly oriented liquidcrystals, higher optical scattering, and lower switching voltages.However, some polymers can exert strong “anchoring” forces on the liquidcrystals inside the droplets which may increase the threshold voltagerequired for complete switching. In some embodiments, the polymer usedin a PDLC material has a refractive index from about 1.52 to about 1.75to match that of the liquid crystal in share mode.

Another kind of electronically switchable material useful for theswitchable privacy film is an electrochromic system. Electrochromicsystems comprise materials that undergo color changes under an appliedelectric field due to occurrence of reversible oxidation-reductionreactions involving chromophores present in the layer between thetransparent electrodes. Such materials can switch between a clear orrelatively low-absorbance state and a highly-colored high-absorbancestate. Materials typically used in electrochromic systems includesurface-bound viologen dyes, phenothiazines, diarylethenes, andconducting polymers such as polythiophenes. In general, application ofthe external electric field produces the color change which persistsuntil the field is removed, at which point the system reverts to thezero-field state. Many electrochromic materials are colorless in theabsence of the electric field and switch to the highly colored statewhen the field is applied, but some systems are known that demonstratethe opposite behavior. Photo/electrochromic systems are also known,which materials can switch between a clear state and a highly coloredstate upon exposure to UV radiation, then be switched back to the clearstate by application of an electric field. Exemplary electrochromicsystems are described in U.S. Pat. No. 6,301,038, U.S. Pat. No.6,870,657, US 2010/0315693, and Y. Ding et al, J. Mater. Chem. 2011, 21,11873.

The electronic stimulus that enables switching for the privacy filmdisclosed herein originates from the pair of opposing transparentelectrodes. The transparent electrodes are substantially optically clearsuch that when viewing an object through the transparent electrodes,little or no distortion of the object is observed, or some acceptablelevel of distortion is observed. In some embodiments, a suitabletransparent electrode exhibits little or no haze, meaning it may have ahaze value not greater than about 10%, not greater than about 5% or notgreater than about 2%. In some embodiments, the transparent substratehas high light transmittance of from about 80 to about 100% over atleast a portion of the visible light spectrum (about 400 to about 700nm). The distance between the two opposing transparent electrodes istypically from about 25 to about 150 um.

In some embodiments, one or both of the transparent electrodes comprisesa conductive layer disposed on a transparent substrate. FIG. 5 shows aschematic cross sectional view of exemplary electronically switchableprivacy film 50 comprising optically transparent microstructured layer53 disposed between opposing transparent electrodes 52. The opticallytransparent microstructured layer comprises plurality of microstructuredribs 54 and channels disposed between the ribs and comprisingelectronically switchable material 55. Each transparent electrode 52comprises conductive layer 58 disposed on transparent substrate 57 withthe conductive layer adjacent optically transparent microstructuredlayer 53.

The conductive layer may comprise a conductive metal oxide such asindiumtin oxide (ITO), indium-doped zinc oxide, fluorine-doped tin oxide,conductive polymer such as polyaniline orpoly(ethylenedioxythiophene)/polystyrenesulfonate, nanocarbons such ascarbon nanotubes or graphene, printed or self-assembled metal grids, ormetallic nanowires, or combinations thereof. In some embodiments, theconductive layer comprises silver nanowires. The thickness of theconductive layer may be less than about 500 nm. In some embodiments, theconductive layer is disposed in some discontinuous form across a surfaceof the transparent substrate, forming a pattern comprising transparentconductive regions and transparent non-conductive regions.

In some embodiments, the transparent electrode comprises metallicnanowires disposed on a transparent substrate, and a polymeric overcoatlayer is disposed on the metallic nanowires opposite the transparentsubstrate. Such transparent electrodes are described in U.S. Ser. No.61/475,860 to Pellerite et al., filed Apr. 15, 2011. For example, thetransparent electrode may comprise a silver nanowire layer exhibitingsheet resistance of 50-150Ω/square, overcoated with a layer of polymerto protect the silver from oxidation and to enhance adhesion ofsubsequently-applied optically transparent layer. In addition, thesilver nanowire-based transparent electrodes can offer high transmissionlevels at lower sheet resistance in comparison with other conductivematerials.

The polymeric overcoat layer may comprise the reaction product of amultifunctional (meth)acrylate, such as the reaction product of amultifunctional (meth)acrylate and a urethane (meth)acrylate oligomer.In some embodiments, the polymeric overcoat layer comprises a polymersuch as methyl (meth)acrylate polymer and the reaction product of amultifunctional (meth)acrylate. Particular examples of materials whichmay be used in the polymeric overcoat layer include pentaerythritoltriacrylate (SR 444C from Sartomer Co.), hexanediol diacrylate, urethaneacrylate oligomers (CN 981 B88 from Sartomer Co.), Ucecoat® 7655 and7689 from Cytec Industries, polymethylmethacrylates (for exampleElvacite® 2041 available from Lucite International, Inc.), polystyrenes,and polyvinylbutyrals (for example Butvar® polymers available fromSolutia Inc.). The polymeric overcoat layer may comprise nanoparticleshaving a diameter from about 10 to about 500 nm, at a weight ratio ofabout 85:15 to about 25:75 polymer nanoparticles. In general, thethickness of the polymeric overcoat layer is from about 50 nm to about 1um.

As described in Pellerite et al., the polymeric overcoat layer maycomprise nanoparticles selected from the group consisting of antimonytin oxide, zinc oxide and indium tin oxide; and the sheet resistance ofthe polymeric overcoat layer disposed on the transparent substratewithout the conductive layer is greater than about 10⁷Ω/sq.

The transparent substrate can comprise any useful material such as, forexample, polymer, glass, ceramic, metal, metal oxide, or a combinationthereof. Examples of polymers that may be used as the transparentsubstrate include thermoplastic polymers such as polyolefins,poly(meth)acrylates, polyamides, polyimides, polycarbonates, polyesters,and biphenyl- or naphthalene-based liquid crystal polymers. Furtherexamples of useful thermoplastics include polyethylene, polypropylene,polystyrene, poly(methylmethacrylate), bisphenol A polycarbonate,poly(vinyl chloride), polyethylene terephthalate, polyethylenenaphthalate, cellulose acetates and poly(vinylidene fluoride). Some ofthese polymers also have optical properties (e.g., transparency) thatmake them especially well-suited for certain display applicationswherein they would support a patterned conductor, such aspolycarbonates, and/or polyesters. The transparent substrate may haveany useful thickness, ranging from about 5 μm to about 1000 μm.

The electronically switchable privacy film comprises exposed conductivematerial on both the top and bottom of the film to enable electricalcontact via silver paste or another suitable conductor material with thetransparent electrodes. A positive bias is applied to one conductor,while a negative bias (or ground terminal) is applied to the otherconductor, or vice versa. The potential difference between the twotransparent electrodes enables the electric field which is used toenergize the electronically switchable material for switching betweenprivacy and share modes.

Also disclosed herein is an electronically switchable privacy filmdevice comprising the electronically switchable privacy film andcircuitry for supplying the electric field. Circuitry may includetransformers, amplifiers, rectifiers, diodes, resistors, capacitors,transistors and the like.

Also disclosed herein is a display device comprising an electronicallyswitchable privacy film, as described herein. In general, the displaydevice comprises some type of light transmissive display panel such as aliquid crystal display (LCD) panel. LCD devices typically comprise anouter substrate or light output substrate adjacent the lighttransmissive display panel and providing a viewing surface.

In some embodiments, the electronically switchable privacy film isdisposed on the viewing surface, for example, as applied by a consumer.For example, the device could be hung on the front of the display usingan additional bezel with built-in circuitry required to operate thedevice. The bezel may include built-in circuitry as required to operatethe device. Alternatively, the bezel may simply provide a means forattaching the electronically switchable privacy film to the displaydevice. In this embodiment, the circuitry required to operate theelectronically switchable privacy film may be a toggle on a cord thatengages with a USB port of the display device. Alternatively, thesoftware of the display device, for example by means of a key stroke(s)or a mouse click, could control the voltage between privacy and sharemode. In another embodiment, the electronically switchable privacy film20 may be attached to the display using an optically clear adhesive 55,such as shown in FIG. 9.

The circuitry is an integral part of the device construction. In any ofthe above embodiments, it is possible to split the “hot lead” positivebias from the AC receptacle of a computer monitor into two wires, onegoing into the display, and the other going to the positive contact ofthe electronically switchable privacy film. The negative bias electrodecan be attached to a metal ground. Alternately, power can be drawn froma battery, or a USB port rated at 5V, 500 milliamps. The voltage can besuitably upconverted using transformer circuitry to generate asufficient high voltage, low current switching waveform that will enablecomplete switching of the electronically switchable material. In the“on” state (share mode), the current used to operate the display devicecan be very low, on the order of 1-3 milliamps. Thus, using a voltageequal to 120V, the total power consumed would be on the order ofhundreds of milliwatts, if share mode is kept on.

A square wave frequency pattern may be used and can provide the highestefficiency in switching behavior. This is because a square wave powersource reverses its polarity almost instantaneously, such that liquidcrystals do not have time to switch between distorted and alignedstates, and the match between n_(o) and n_(p) is maintained during eachcycle of the applied field; see, for example, U.S. Pat. No. 5,156,452(Drzaic et al.).

FIG. 7 shows images of an exemplary electronically switchable privacyfilm used with a standard eye chart. In the privacy mode, as shown inthe upper left hand quadrant, an observer positioned at some off-axisangle relative to the normal of the privacy film is not able to viewletters behind the film. An electronic switch is activated such that theprivacy film is electronically switched to a share mode, and as shown onthe right, letters behind the film can be seen. From an on-axis position(zero degree angle relative to the normal of the film), letters behindthe film can be seen in both privacy and share modes regardless ofwhether or not the privacy film has been electronically switched.

FIG. 8 shows schematic representations of an exemplary electronicallyswitchable privacy film used in conjunction with an electronic displaydevice. In this representation, either the privacy film is disposed onthe viewing surface of the device, or it is contained within the device,for example, between the liquid crystal display panel and a substratethat forms the outer viewing surface. In the privacy mode, as shown inthe upper left hand quadrant of the representation, an observerpositioned at some off-axis angle relative to the normal of the viewingsurface is not able to view contents being displayed. The user of thedevice activates an electronic switch such that the privacy film iselectronically switched to a share mode, shown on the right, and theobserver is able to view contents being displayed without having toreposition himself. The user is positioned on-axis or at zero degreeangle relative to the normal of the viewing surface, and contents beingdisplayed by the device are viewable in both privacy and share modesregardless of whether or not the privacy film has been electronicallyswitched.

EXAMPLES Preparation of Transparent Electrodes

Transparent electrodes were prepared as described in Examples 15-18 ofU.S. Ser. No. 61/475,860 to Pellerite et al., filed Apr. 15, 2011. Asilver nanowire ink prepared using the methods disclosed in Example 5 ofWO 2008/046058 (Allemand et al.) was coated on 5 mil PET film (Melinex®618 from DuPont Teijin Films) using a 9 inch die coater operating at aweb speed of 15 ft/min, ink flow rate of 15.5 cc/min, drying ovenairflow 19.7 m/sec, and drying oven temperatures of 105° F. (Zone 1) and175° F. (Zone 2) and 250° F. (Zone 3). Sheet resistance of the resultingcoating was 60-100Ω/sq using a contactless probe (Delcom 717RNon-Contact Conductance Monitor from Delcom Products Inc.), andtransmission and haze measured on a Haze-Gard Plus haze meter(BYK-Gardner USA) were found to be 90-92% and 1.4-1.6%, respectively.

A polymeric overcoat solution was prepared as follows. A concentrate wasprepared by dissolving an 85:15 (w:w) mixture of pentaerythritoltriacrylate (SR 444 from Sartomer Co.) and methyl methacrylate polymer(Elvacite® 2041 from Lucite International, Inc.) in acetone to 10 wt %total solids. Photoinitiator (Irgacure® 651 from Ciba SpecialtyChemicals) was added at 0.2 wt % total solids. The polymeric overcoatsolution was prepared by combining ATO Sol (nominal 30 wt. % antimonytin oxide (ATO) nanoparticles in IPA from Advanced Nano Products, Korea)and the above 10 wt. % concentrate, in amounts to give a 25:75 weightratio of ATO:organic solids, and diluting the resulting mixture to 5 wt% total solids using 1:1 IPA:diacetone alcohol.

The polymeric overcoat solution was coated on top of the conductorlayer. Coating was performed on a 9 inch die coater used for the inkcoating, using the above oven and air flow settings, web speed of 20ft/min, solution flow rates of 18 cc/min, UV plate temperature of 70°F., nitrogen atmosphere, and 100% UV lamp power. Transmission and hazewere measured at 87.5 and 1.17%, respectively, using a BYK-GardnerHazeGard Plus. The sheet resistance was measured at 72.3Ω/sq using theDelcom system described above.

Optically Clear Microstructured Layer

Properties of optically clear microstructured layers employed in theexamples are shown in Table 1.

TABLE 1 Properties of Optically Clear Microstructured Layers Rib, RibChannel Channel Rib Channel Aspect Aspect Height Pitch Width Width RatioRatio Example H P W P − W H/W H/(P − W) 1 75 33 30 3 2.5 25 Comp. 1 2535 25 10 1 2.5 Comp. 2 4 6 4 2 1 2 Comp. 3 75 33 30 3 2.5 25 2 75 33 303 2.5 25Electronically Switchable Material

Properties of electronically switchable materials employed in theexamples are shown in Table 2.

TABLE 2 Properties of Electronically Switchable Materials 1:2 Mixture,BLO-36, used GHLC of in Comparative Property MDA-04-927 ZLI-4727 Table 2Example 3 Δε* 68.2 6.00 26.7 16.6 ε_(∥)* 78.8 9.60 32.6 21.7 ε⊥* 10.63.60 5.93 5.06 n_(e)** 1.75 1.63 1.67 1.79 n_(o)** 1.52 1.50 1.51 1.52Δn** 0.23 0.13 0.16 0.27 *Measured at 1 kHz and 20° C. **Measured at 589nm and 20° C.

Example 1

A microstructured film was prepared by molding and UV curing an acrylateresin formulation on a first transparent electrode using a roll-to-rollweb coating process. The acrylate resin is described in US 2007/0160811A1 (Gaides et al.) The first transparent electrode was prepared asdescribed above, and the microstructured film was formed on thepolymeric overcoat. The web speed used was 10 ft/min, with theimprinting tool operating at 110° F., curing using two banks of Fusionhigh intensity UV D-bulb lamps operating at 100% power. An annealingoven was set for 200° F., at a four foot length. The resulting structureof the cured acrylate consisted of regularly spaced channels each havinga nominally rectangular cross-section, as described in Table 1. Thechannels were filled with the electronically switchable material GHLC-1described in Table 3, which was heated to 90° C. in order to reduceviscosity.

TABLE 3 Guest-Host Liquid Crystal Composition (GHLC-1) Material Weight %MDA-04-927 (Merck KGaA) 35 ZLI-4727 (Merck KGaA) 65

A second transparent electrode was laminated over the top of the filledchannels using a flat-bed laminator operating at 0.167 inches/minute,and a nip pressure of 25 psi. The top sheet (second transparentelectrode) was offset cross-web from the bottom sheet (first transparentelectrode), to enable easier access to electrical contact pads. Excessswitchable material was left at the start and end of the lamination toprevent air bleed and maximize capillary filling of the channels. Acolloidal dispersion of silver particles (Ted Pella, Inc.) was appliedonto the exposed electrode pads to allow for electrical contact to thetransparent conductor. The film construction was left to equilibrate toroom temperature before optical testing. Testing was performed byapplying positive and negatively charged bias voltages to the driedsilver paste contacts from an electrical power source via two alligatorclips.

Light transmission as a function of viewing angle was measured for thefilm construction using an Eldim 80 Conoscope (Eldim Corp., France). Thefilm was placed on top of a diffusively transmissive hollow light box.The luminance (cd/m², or “nits”, i.e. brightness) profiles of the lightbox with the film was measured. The diffuse transmission of the lightbox can be described as Lambertian. The light box was a six-sided hollowcube measuring approximately 12.5 cm×12.5 cm×11.5 cm (L×W×H) made fromdiffuse polytetrafluoroethylene (PTFE) plates of ˜6 mm thickness. Oneface of the box was chosen as the sample surface. The hollow light boxhad a diffuse reflectance of ˜0.83 measured at the sample surface (e.g.˜83%, averaged over the 400-700 nm wavelength range). During thetesting, the box was illuminated from within through an approximately 1cm circular hole in the bottom of the box (opposite the sample surface,with the light directed toward the sample surface from inside). Theillumination was provided using a stabilized broadband incandescentlight source attached to a fiber-optic bundle used to direct the light(Fostec DCF-II with a 1 cm diameter fiber bundle extension fromSchott-Fostec LLC, Marlborough, Mass. and Auburn, N.Y.). An Eldim 80Conoscope was used to measure the luminance (brightness) profiles of thediffuse light source both with and without the light control filters. Aslice along the meridian of the conoscope image shows the transmissionas a continuous function of viewing angle and this data is shown in FIG.6.

Light transmission was determined as a function of viewing angle for theswitchable privacy filter oriented with the louvers facing up (closestto the Conoscope measurement), in both privacy and share mode. Acommercially available light control film (Vikuiti™ advanced lightcontrol film, available from 3M Company) was used as a reference tocompare against the privacy mode of the switchable light control filter.Normalized transmission was measured by dividing the luminance of thelight control films in each mode by the luminance of the hollow lightbox.

Transmission and haze data were measured using a Haze-Gard Plusinstrument, with a measurement area of 18 mm. The Haze-Gard Plustransmittance measurement is an average of the total transmittance oflight across 380-720 nm, weighted according the CIE Illuminant “C”. Thefilm construction was clipped to a rotational stage and placed midwaybetween the light source and detector. Data was taken at 15 degreeintervals up to 60 degrees and are reported in Table 4.

TABLE 4 Optical Properties of Switchable Privacy Film of Example 1Privacy Mode Share Mode (Off State, 0 V) (On State, 120 V*) View Trans-Trans- ΔT ΔH Angle mission Haze mission Haze (T_(on) − (H_(on) − (°) (%)(%) (%) (%) T_(off)) H_(off)) 0 48 7.0 50 9.0 2.0 2.0 15 31 9.0 37 116.0 2.0 30 6.0 53 18 18 12 −35 45 2.0 63 12 14 10 −49 60 1.0 57 9.0 188.0 −39 *sine wave 60 Hz AC

Comparative Example 1

An electronically switchable privacy film was prepared as described forExample 1 except the microstructured film consisted of regularly spacedchannels as described in Table 1. The liquid crystal material used wasZLI-4727, without the chiral dopant MDA-04-927. Testing was carried outusing the Haze-Gard Plus haze meter as described for Example 1; data arereported in Table 5. In the privacy mode, the transmission was higherthan Example 1 at viewing angles of 30° and 40°. Further, the differencein transmission at these angles between privacy mode and share mode wasmuch lower than Example 1.

TABLE 5 Optical Properties of Switchable Privacy Film of ComparativeExample 1 Privacy Mode Share Mode (Off State, 0 V) (On State, 120 V*)View Trans- Trans- ΔT ΔH Angle mission Haze mission Haze (T_(on) −(H_(on) − (°) (%) (%) (%) (%) T_(off)) H_(off)) 0 38 13 39 11 1.0 −2.015 27 19 30 16 3.0 −3.0 30 15 29 18 18 3.0 −11 45 8.0 24 10 16 2.0 −8.060 6.0 28 6.0 16 0.0 −12 *sine wave 60 Hz AC

Comparative Example 2

A comparative film was prepared as described for Example 1 except themicrostructured film consisted of regularly spaced channels as describedin Table 1. ZLI-4727 was loaded into the channels without chiral dopant“MDA-04-927.” Here the height of the channels did not allow enoughloading of liquid crystals to effectively hide the display in theprivacy mode. In share mode, some switching of the liquid crystallinematerial was observed, but the effect was not significant since theprivacy mode was ineffective.

Comparative Example 3

A comparative film was prepared as described for Example 1 except thatthe electronically switchable material did not have a dichroic dye, nordoes it have as high of a dielectric anisotropy as GHLC-1. Theswitchable material was a liquid crystalline material, from EMIndustries, Hawthorne, N.Y., available under the trade designation“BLO-36”, having electronically switchable properties as depicted inTable 2. The microstructured film consisted of regularly spaced channelsas described in Table 1. Testing was carried out using the Haze-GardPlus haze meter as described for Example 1; data are reported in Table6. Although the switch in transmission was high (15%) the transmissionin privacy mode was high (39%) at a viewing angle of 45°. Thus, thisexample exhibited undesirable optical properties and obviated the needfor the inclusion of dichroic dye to block more light in privacy mode.

TABLE 6 Optical Properties of Switchable Privacy Film of ComparativeExample 3 Privacy Mode Share Mode (Off State, 0 V) (On State, 120 V*)View Trans- Trans- ΔT ΔH Angle mission Haze mission Haze (T_(on) −(H_(on) − (°) (%) (%) (%) (%) T_(off)) H_(off)) 0 62 38 67 33 5.0 −5.015 50 40 61 38 11 −2.0 30 43 53 59 37 16 −16 45 39 59 55 37 16 −22 60 3071 43 54 13 −16 *sine wave 60 Hz AC

Table 7 summarizes properties and performance of privacy films preparedaccording to Example 1 and Comparative Examples 1-3.

TABLE 7 Properties and Performance of Privacy Films Rib, % TransmissionChannel Aspect Ratio Privacy Share Height Rib Channel Mode Mode ExampleH H/W H/(P − W) Δε at 45° at 45° Delta 1 75 2.5 25 27 2.0 12 10 Comp. 125 1.0 2.5 27 8.0 10 2.0 Comp. 2 4.0 1.0 2.0 27 N/M* N/M N/M Comp. 3 752.5 25 17 39 55 16 *not measured - privacy mode not observed

Example 2

An electronically switchable privacy film was prepared as described forExample 1 except GHLC-1 described by Table 2 was replaced with a UVcurable guest-host liquid crystal mixture GHLC-2 reported in Table 8with subsequent curing in a custom-built UV radiation chamber at 3mW/cm² for 30 minutes to form a polymer-dispersed liquid crystalformulation. Testing was carried out as described for Example 1;Haze-Gard Plus data are reported in Table 9. Performance was similar toExample 1, except for a slightly less transmissive share mode from the45° viewing angle.

TABLE 8 Guest-Host Liquid Crystal Composition (GHLC-2) Material Weight %MDA-04-927 26.6 ZLI-4727 53.3 n-butyl methacrylate (n-BMA, Aldrich) 15.4ethylene glycol diacrylate (EGDA, Aldrich) 4.60 Irgacure ® 819 0.30

TABLE 9 Optical properties of switchable privacy film of Example 2Privacy Mode Share Mode (Off State, 0 V) (On State, 120 V*) View Trans-Trans- ΔT ΔH Angle mission Haze mission Haze (T_(on) − (H_(on) − (°) (%)(%) (%) (%) T_(off)) H_(off)) 0 54 12 55 12 1.0 00 15 33 9.0 38 9.0 5.00.0 30 5.0 58 16 23 11 −35 45 2.0 76 11 23 9.0 −53 60 1.0 81 6.0 31 5.0−50 *sine wave 60 Hz AC

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations can besubstituted without departing from the spirit and scope of theinvention.

What is claimed is:
 1. An electronically switchable privacy filmcomprising: a pair of mutually opposing transparent electrodes; anoptically transparent microstructured layer disposed between thetransparent electrodes, the microstructured layer comprising a pluralityof microstructured ribs extending across a surface thereof such that themicrostructured ribs form an alternating series of ribs and channels;electronically switchable material disposed in the channels, theelectronically switchable material being capable of modulation betweenhigh and low absorption states upon application of an electric fieldacross the transparent electrodes; wherein: when the electric field isnot applied, the film is in a privacy mode such that it has a lighttransmission of less than about 10% at a viewing angle of 30°; when theelectric field is applied, the film is in the share mode such that ithas an increase in light transmission and the difference in transmissionbetween the privacy mode and share mode is at least 5% for viewingangles from about 30 to about 45°, the film has a light transmission ofat least about 25% in share and privacy modes at viewing angles from 0to about 15°.
 2. The electronically switchable privacy film of claim 1,wherein the electronically switchable material comprises a liquidcrystal or electrochromic material.
 3. The electronically switchableprivacy film of claim 1, wherein the electronically switchable materialcomprises a mixture of liquid crystals and dichroic dye.
 4. Theelectronically switchable privacy film of claim 1, wherein theelectronically switchable material comprises a mixture of chiral liquidcrystals and dichroic dye.
 5. The electronically switchable privacy filmof claim 1, wherein the electronically switchable material comprises amixture of nematic liquid crystals and dichroic dye.
 6. Theelectronically switchable privacy film of claim 1, wherein theelectronically switchable material comprises a mixture of chiral liquidcrystals, nematic liquid crystals and dichroic dye.
 7. Theelectronically switchable privacy film of claim 6, wherein theelectronically switchable material has a pitch length of about 800 toabout 1500 nm.
 8. The electronically switchable privacy film of claim 1,wherein the electronically switchable material comprises liquid crystalsand dichroic dye dispersed in a polymer matrix.
 9. The electronicallyswitchable privacy film of claim 1, wherein a magnitude of thedielectric anisotropy for the electronically switchable material isgreater than about
 20. 10. The electronically switchable privacy film ofclaim 1 wherein the electronically switchable material comprises anelectronically switchable material having a dielectric anisotropy of atleast 20, 30, 40, 50, or
 60. 11. The electronically switchable privacyfilm of claim 1, wherein the electronically switchable material has arefractive index from about 1.52 to about 1.75.
 12. The electronicallyswitchable privacy film of claim 1, wherein each rib has height H, widthW and rib aspect ratio H/W greater than about 1.5.
 13. Theelectronically switchable privacy film of claim 1, wherein each channelhas height H, width Y and channel aspect ratio H/Y greater than
 5. 14.The electronically switchable privacy film of claim 1, wherein theoptically transparent microstructured layer has a refractive index fromabout 1.48 to about 1.75.
 15. The electronically switchable privacy filmof claim 1, wherein the difference between the refractive indices of theelectronically switchable material and the optically transparentmicrostructured layer is less than about 0.05 when the privacy film isin the share mode.
 16. The electronically switchable privacy film ofclaim 1, wherein the difference between the refractive indices of theelectronically switchable material and the optically transparentmicrostructured layer is greater than about 0.05 when the privacy filmis in the privacy mode.
 17. The electronically switchable privacy filmof claim 1, wherein each transparent electrode comprises a conductivelayer disposed on a transparent substrate, and each conductive layer isadjacent opposing major surfaces of the optically transparentmicrostructured layer.
 18. A display device comprising: a lighttransmissive display panel, a light output substrate adjacent the lighttransmissive display panel, the light output substrate comprising aviewing surface opposite the light transmissive display panel, and theelectronically switchable privacy film of claim 1 disposed on theviewing surface.
 19. A display device comprising: a light transmissivedisplay panel, a light output substrate adjacent the light transmissivedisplay panel, the light output substrate comprising a viewing surfaceopposite the light transmissive display panel, and the electronicallyswitchable privacy film of claim 1 disposed between the lighttransmissive display panel and the light output substrate.
 20. Thedisplay device of claim 19, wherein the light output substrate comprisesa touch screen.